Expression of tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) in minor salivary glands and saliva

Objective: The aim of this study was to characterize the baseline expression of tumor necrosis factor (tnf)-related apoptosis inducing ligand (TRAIL) in minor salivary glands, gingiva and saliva from healthy individuals. Design: Minor salivary gland and gingival tissues were used in the study for immunohistochemical staining. An enzyme-linked immunosorbent assay was used to measure the levels of TRAIL in unstimulated saliva and parotid saliva collected from non-smoking individuals. The salivary levels of TRAIL are presented as secretory output. Results: Parotid saliva showed higher secretory output (327.8 +/- 41.6 pg/min) for TRAIL compared to unstimulated saliva (212.3 +/- 32.1 pg/min; p = 0.041). For unstimulated saliva, the young female subjects had the lowest secretory output (119 +/- 17.2 pg/min) compared to elderly females (275 +/- 62.18 pg/min; p = 0.046) and young males (294.4 +/- 50.2 pg/min; p = 0.021). The ductal cells of salivary glands exhibited the strongest positivity for TRAIL, whereas mucous cells showed no staining for TRAIL. Serous cells displayed an intermediate staining. Gingival tissues showed gradually decreasing staining towards the basal layer. Conclusions: The current study shows that TRAIL is not only expressed by immune cells, but also by the epithelial cells of salivary glands. Saliva contains high concentrations of soluble TRAIL that suggest roles of this protein in the apoptosis of tumor cells.